1. Technical Field
The present invention relates to a photographic lens system made by assembling five lenses and, more particularly, to a photographic lens system enabling reduction in tightness of manufacturing tolerance, which is composed of five lenses, and in which refractivities, shapes, ABBE numbers, etc. of respective lenses are appropriately designed, thereby realizing lightness and smallness of the lenses, and enabling reduction in tightness of manufacturing tolerance of the lenses, and realizing high reproducibility of performance of the lenses.
2. Description of the Related Art
In recent years, the use of mobile phone cameras and digital cameras is increased and services provided by the mobile phone cameras and digital cameras are required to be diversified, for example functions such as photographing, picture transmission or communication are strongly required.
Particularly, photographic lens units of mobile phone cameras are required to provide improved and diverse functions. To this end, a new concept mobile phone, which is formed by combining a digital camera technique with a mobile phone technique and is a so-called “camera phone” (or camera mobile phone), has been proposed and spotlighted. To realize the requirements of high efficiency of the camera phone, a camera module in which an image pickup device having at least 3-megapixel size has been actively studied recently.
To realize the requirements of high definition and high efficient function higher than at least a 3-megapixel size, at least three to five lenses are used in the camera module of the mobile phone camera.
Examples of conventional techniques proposed to realize the requirements of high definition and high efficiency are referred to the following patent documents.
U.S. Pat. No. 8,395,851 discloses an optical lens system having five lenses sequentially arranged from an object side, in which a second lens has negative refractivity, and which is configured to form a predetermined focal distance, a predetermined radius of curvature, a predetermined ABBE number, etc.
Korean Patent No. 10-1158419 discloses a lens system composed of five lenses, in which a second lens has negative refractivity, and the five lenses are configured to realize respective predetermined conditions in the focal distance, the radius of curvature, etc.
Further, Korean Patent No. 10-12765434 discloses a photographic optical lens system, which is composed of five lenses, and in which a second lens has negative refractivity.
In the related art photographic lens systems each composed of five lenses, it is typical that the second lens has the negative refractivity, as described above. When the second lens has the negative refractivity, the central portion of the lens is thinner than the peripheral portion, so the flowability of resin during an injection molding process of manufacturing lenses is reduced, and this reduces the reproducibility of performance of products.
In other words, the above-mentioned conventional techniques are problematic in that, during a process of manufacturing lenses, resin does not easily flow, so reproducibility of performance of lenses is reduced, and this makes the manufacturing tolerance of the lenses tight. Particularly, when a micro-lens system is a tight tolerance system, the performance varies product by product, so it is required to reduce the tightness of manufacturing tolerance of lenses and to increase the reproducibility of performance of the lenses by an easy method.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.